METHOD FOR SEPARATING WATER AND CONTAMINANTS FROM VALUABLE OR HARMFUL LIQUIDS
20230264115 · 2023-08-24
Inventors
Cpc classification
B01D1/14
PERFORMING OPERATIONS; TRANSPORTING
B01D5/006
PERFORMING OPERATIONS; TRANSPORTING
C02F2303/22
CHEMISTRY; METALLURGY
International classification
Abstract
The present disclosure is a method of removing water and contaminants from an aqueous feed stream comprising a water soluble process liquid. Embodiments of the method may include splitting the method into stages, vaporising the process liquid by direct contact with a heated heating fluid, removing precipitated contaminants by chemical means, and treating the heating fluid to maintain or enhance its properties.
Claims
1. A method of removing contaminants, including dissolved contaminants, from a feed stream, said feed stream comprising water and said contaminants and a process liquid that is water soluble and less volatile than water, said method comprising the following steps: heating a heating fluid comprised of components that are immiscible with a salt solvent and less volatile than the process liquid to produce a heated heating fluid; bringing at least a portion of the feed stream into contact with at least a portion of the heated heating fluid at one or more places that are upstream of and/or within a flash separator to vaporise at least a portion of the process liquid thereby causing at least a portion of the dissolved contaminants to form precipitated solid matter; enabling at least a portion of the heating fluid to mix with at least a portion of the precipitated solid matter thereby producing a depleted mixture that comprises at least a portion of the heating fluid and at least a portion of the precipitated solid matter; and bringing the salt solvent into contact with at least a portion of the depleted mixture whereby said salt solvent dissolves at least a portion of the precipitated solid matter, to create a waste solution that comprises at least a portion of the dissolved contaminants.
2. A method of removing contaminants, including dissolved contaminants, from a feed stream, said feed stream comprising water and said contaminants and a process liquid that is water soluble and less volatile than water, said method comprising the following steps: applying a concentration process to remove water from at least a portion of the feed stream to produce a Stage A output stream having a concentration of process liquid that is higher than that of the feed stream; heating a heating fluid comprised of components that are immiscible with a salt solvent and less volatile than the process liquid to produce a heated heating fluid; bringing at least a portion of the Stage A output stream into contact with at least a portion of the heated heating fluid at one or more places that are upstream of and/or within a flash separator to vaporise at least a portion of the process liquid thereby causing at least a portion of the dissolved contaminants to form precipitated solid matter; enabling at least a portion of the heating fluid to mix with at least a portion of the precipitated solid matter thereby producing a depleted mixture that comprises at least a portion of the heating fluid and at least a portion of the precipitated solid matter; and bringing the salt solvent into contact with at least a portion of the depleted mixture, whereby said salt solvent dissolves at least a portion of the precipitated solid matter to create a waste solution that comprises at least a portion of the dissolved contaminants.
3. A method of removing contaminants, including dissolved contaminants, from a feed stream, said feed stream comprising water and said contaminants and a process liquid that is water soluble and less volatile than water, said method comprising the following steps: heating a concentrated process liquid to produce heated concentrated process liquid; bringing at least a portion of the feed stream into contact with at least a portion of the heated concentrated process liquid at one or more places that are upstream of and/or within a Stage B separation vessel to vaporise a portion of the process liquid thereby producing an unvaporised liquid that comprises at least a portion of the dissolved contaminants; enabling at least a portion of the unvaporised liquid to mix with at least a portion of the concentrated process liquid thereby producing a Stage B to C stream that comprises at least a portion of the process liquid and at least a portion of the dissolved contaminants; heating a heating fluid comprised of components that are immiscible with a salt solvent and less volatile than the process liquid to produce a heated heating fluid; bringing at least a portion of the Stage B to C stream into contact with at least a portion of the heated heating fluid at one or more places that are upstream of and/or within a flash separator to vaporise at least a portion of the process liquid thereby causing at least a portion of the dissolved contaminants to form precipitated solid matter; enabling at least a portion of the heating fluid to mix with at least a portion of the precipitated solid matter thereby producing a depleted mixture that comprises at least a portion of the heating fluid and at least a portion of the precipitated solid matter; and bringing the salt solvent into contact with at least a portion of the depleted mixture whereby said salt solvent dissolves at least a portion of the precipitated solid matter, thereby creating a waste solution that comprises at least a portion of the dissolved contaminants.
4. The method as claimed in claim 2 wherein the concentration process comprises heating the feed stream to a temperature sufficient to vaporise and remove at least a portion of the water.
5. The method as claimed in claim 3 further including the step of regulating the flow of the Stage B to C stream to limit the accumulation of at least a portion of the dissolved contaminants in the Stage B separation vessel.
6. The method as claimed in claim 1 further including the step of applying one or more heating fluid treatment means to decontaminate at least a portion of the heating fluid.
7. The method as claimed in claim 1 further including the step of applying one or more heating fluid treatment means to at least a portion of the heating fluid to modify one or more properties of the heating fluid, including but not limited to density, vapour pressure, viscosity, thermal stability, pH, solubility, heat capacity, thermal conductivity, corrosivity, toxicity, and flammability.
8. The method as claimed in claim 6 wherein the one or more heating fluid treatment means include adding one or more substances and mixing said added substances with at least a portion of the heating fluid to achieve any one or more of the following effects: to cause a reaction with carbonate and/or bicarbonate contaminants thereby producing water and/or carbon dioxide; to reduce the oxygen content of the heating fluid; to remove and/or dissolve and/or destroy asphaltenes, resins, gums and/or sludges; to prevent or inhibit the formation of, or enable the removal of, scale or fouling deposits on metal surfaces; to break-down, suppress, or inhibit the formation of, emulsions or foam; to reduce the cloud point and/or freezing point of liquid contaminants; to neutralise acids and/or increase alkalinity and/or inhibit corrosion; and to react with dissolved contaminants and cause precipitation of solid matter that can be removed by mechanical means of separation.
9. The method as claimed in claim 6 wherein the one or more heating fluid treatment means include heating at least a portion of the heating fluid to vaporise and thereby remove at least a portion of the liquid contaminants.
10. The method as claimed in claim 6 wherein the one or more heating fluid treatment means include removing contaminating particles of solid matter from at least a portion of the heating fluid by mechanical means of separation including but not limited to any one or more of: centrifuging, settling, clarifying, filtering, and hydrocycloning.
11. The method as claimed in claim 6 wherein the one or more heating fluid treatment means include adding one or more substances and mixing said added substances with at least a portion of the heating fluid to cause a reaction that converts at least a portion of the organic salt contaminants into volatile organic acids and vaporising at least a portion of said volatile organic acids.
12. The method as claimed in claim 7 wherein the one or more heating fluid treatment means include adding one or more substances and mixing said added substances with at least a portion of the heating fluid to modify one or more properties of the heating fluid, including but not limited to density, vapour pressure, viscosity, thermal stability, pH, solubility, heat capacity, thermal conductivity, corrosivity, toxicity, and flammability.
13. The method as claimed in claim 1 wherein the heating fluid comprises components that are immiscible with the process liquid.
14. (canceled)
15. The method as claimed in claim 1 wherein the process liquid comprises any one or more liquids selected from the group comprising: mono-ethylene glycol; diethylene glycol; triethylene glycol; and amines.
16. The method as claimed in claim 1 wherein the dissolved contaminants comprise any one or more of: monovalent salts including sodium chloride; divalent ions including calcium; and organic acid salts including acetate.
17. The method as claimed in claim 1 wherein at least all but a negligible remnant of the process liquid that contacts the heated heating fluid is vaporised.
18-19. (canceled)
20. The method as claimed in claim 1 wherein the heating fluid comprises one or more liquid components selected from any of the following groups: oils; fatty acids; heat transfer fluids; liquid metals; ionic liquids; and deep eutectic solvents.
21. The method as claimed in claim 1 wherein at least a portion of the salt solvent enters the flash separator and mixes with depleted mixture and dissolves at least a portion of the precipitated solid matter thereby creating a waste solution that comprises at least a portion of the dissolved contaminants.
22. The method as claimed in claim 1 wherein at least a portion of the depleted mixture moves into a solvent wash system wherein at least a portion of the precipitated solid matter dissolves in at least a portion of the salt solvent, thereby creating a waste solution that comprises at least a portion of the dissolved contaminants.
23. (canceled)
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0076]
[0077]
[0078]
[0079]
DETAILED DESCRIPTION
[0080] The present disclosure provides methods that comprise configurations of process stages to achieve the objective of separating water, dissolved salts and other contaminants from a feed stream that comprises a solution of water and water-soluble process liquid such as but not limited to glycols including mono-ethylene glycol (MEG), and amines. In embodiments, the stages may comprise the following processes: Concentration, herein labelled “Stage A”; Flash on Process Liquid, herein labelled “Stage B”; and Flash on Heating Fluid, herein labelled “Stage C”.
[0081]
[0082] In embodiments for a three stage option, the feed stream comprising an aqueous process liquid solution enters Stage A in which water is removed from the feed stream thereby creating a concentrated process liquid solution. For example this stage of the method could include heating the feed stream so as to vaporise at least a portion of the water and separating the vaporised water from the unvaporised portion of the feed stream. The concentrated process liquid produced in Stage A might then flow to Stage B where it is heated and partially vaporised using, for example, a Flash on Process Liquid process in which the vaporisation heat is provided by heating a stream of concentrated process liquid and mixing this heated concentrated process liquid stream with the feed stream. Vapour from Stage B might be condensed to produce an output stream of substantially salt free concentrated process liquid. An unvaporised residual stream of concentrated process liquid containing dissolved and precipitated salts and other contaminants may flow to Stage C. Salts and other contaminants might be removed in Stage C using the Flash on Heating Fluid process in which heated heating fluid provides the heat to vaporise process liquid. The vaporised process liquid in Stage C might be condensed to produce an output stream of substantially salt free concentrated process liquid.
[0083] In the present disclosure, the term “concentrated process liquid” means a liquid having an elevated concentration of process liquid within a range extending from 0.1% higher than the concentration of process liquid in the feed stream 10 up to 100% process liquid.
[0084] Non-limiting examples of the preferred embodiments are illustrated in
Stand-Alone Flash on Heating Fluid
[0085]
[0086] Sufficient heat is added to the heating fluid in heater 24 and/or by heating the heating fluid within flash separator 21 to cause at least a portion of the water and process liquid in stream 10 to vaporise when stream 20 contacts heated heating fluid.
[0087] In embodiments at least all but a negligible remnant, of the process liquid in stream 10 might be vaporised as a result of the contact between stream 10 and the heated heating fluid. In the present disclosure, the term “negligible remnant” means an amount that is not more than the allowable maximum loss of process liquid for the particular application of the present disclosure. For example in MEG reclamation application, if the allowable maximum loss of MEG is 0.5% then the term “at least all but a negligible remnant of the process liquid” means at least 99.5% of the MEG that is in feed stream 10.
[0088] In embodiments, over 95%, or preferably over 98%, of the process liquid in stream 10 might be vaporised as a result of the contact between stream 10 and the heated heating fluid.
[0089] A person skilled in the art will recognise that there are alternative feasible means of heating the heating fluid. In an embodiment at least a portion of the heating fluid might be heated while in the liquid pool of flash separator 21, for example by a submerged tube bundle or heating coils or vessel heating jacket or other type of heating device. This could be in addition to, or instead of, the pumped system shown in
[0090] The following descriptions under the headings: Separation and Removal of Contaminants; Heating Fluid Composition; and Heating Fluid Treatment Means apply to embodiments of the present disclosure including those illustrated in
Separation and Removal of Contaminants
[0091] Vaporised process liquid and optionally vaporised liquid contaminants and optionally vaporised liquid components of the heating fluid, exit the flash separator 21 and flow via stream 26 into condenser system 27 in which separation and condensation of components of the vapour might be achieved using standard methods known to persons skilled in the art. The condenser system 27 might include equipment to enable operation of the flash separator 21 at below atmospheric pressure, for example at less than 0.5 bara, or less than 0.2 bara. Stream 28 might comprise non-condensed gases and vapour that might be subsequently removed. Stream 29 is an output product stream that may comprise concentrated process liquid that is depleted of salts and other contaminants. Stream 30 is optional and may comprise condensed heating fluid which can be subsequently returned to the flash separator 21 liquid pool. Stream 31 is optional and may comprise condensed liquid contaminants that are subsequently removed.
[0092] The Flash on Heating Fluid process removes dissolved contaminants (e.g. salts) by vaporising at least a portion of the liquids that contain the dissolved contaminants thereby causing dissolved contaminants to precipitate and accumulate in the pool of heating fluid in flash separator 21. In embodiments at least all but a negligible remnant, of the process liquid might be removed as vapour from flash separator 21. For the example of a MEG reclamation application, this might provide an effective simple solution to the divalent ion problem. In the present disclosure calcium and other divalent ions which might come out of solution as concentrations reach and exceed solubility limits are surrounded by heating fluid. The MEG molecules have been vaporised hence there is a shortage of MEG available to form the troublesome complex calcium-MEG-chloride compound. This enables calcium chloride and/or other non-troublesome calcium salts to precipitate and, along with precipitated monovalent salts, mix with the heating fluid in the liquid pool in flash separator 21. Calcium chloride is a well-known water soluble salt. The mixture of heating fluid and precipitated solid matter (e.g. salts) that consequently collects in the liquid pool in flash separator 21 is depleted of process liquid, and is herein termed “depleted mixture”.
[0093] In embodiments illustrated in
[0094] In other applications the salt solvent may comprise other liquids (e.g. organic solvents, alcohols, deep eutectic solvents) that are capable of dissolving the particular contaminants that are present in such applications.
[0095] In an embodiment the solvent wash system might be operated at a pressure that is high enough to avoid boiling salt solvent when the depleted mixture contacts the salt solvent in the solvent wash system 40. The boiling could otherwise disrupt operations. Alternatively or in addition the depleted mixture can be cooled before contacting salt solvent in the solvent wash system 40.
[0096] In embodiments, the step of dissolving at least some precipitated salts might be done by temporarily stopping normal operation and adding salt solvent directly to the depleted mixture in the liquid pool in flash separator 21. This may require adjusting the operating temperature and pressure in the flash separator 21 to avoid boiling. The salt solvent would dissolve at least a portion of the precipitated solid matter, thereby creating a waste solution that contains dissolved contaminants and that may be separated from heating fluid and removed from flash separator 21.
[0097] In the Flash on Heating Fluid process the heating fluid might be intentionally repeatedly exposed to a wide range of substances that had originally been in feed stream 10 and have entered flash separator 21. Some of these substances might comprise unwanted contaminants (solid and liquid) that might not be removed in the solvent wash system 40. Some of these contaminants may cause the quality of the heating fluid to degrade. To rectify, or avoid, such degradation the Flash on Heating Fluid process according to one or more embodiments might include one or more heating fluid treatment means (HFTM), details of which are disclosed elsewhere in the present disclosure including under the heading Heating Fluid Treatment Means below, to decontaminate and/or modify the properties of the heating fluid and/or provide other remedial measures to maintain or enhance the condition and performance of the heating fluid. In the non-limiting illustrations in
[0098] While some HFTM may be performed by pumping heating fluid into a HFTS, some other HFTM may be performed by, for example, directly adding chemicals to flash separator 21 via optional stream 45, or into feed stream 10 or at another effective location, and/or removing contaminants directly from flash separator 21. Some contaminants may optionally be drained out of flash separator 21 via stream 47 or be vaporised to flow out of flash separator 21 in stream 26 after which they could be removed via stream 28 and/or stream 31.
[0099] In embodiments, the present disclosure substantially reduces the risk of loss of process liquid in the waste streams with a corresponding reduction in risk of harm to the environment. In embodiments in which at least all but a negligible remnant, of the process liquid is removed as vapour from flash separator 21, there are no means by which a non-negligible amount of process liquid can enter, and be lost with, the waste solutions that contain the contaminants.
[0100] By comparison in the prior art solid waste matter is separated from process liquid using mechanical means (e.g. filter, clarifier, settling tank, centrifuge). This causes the loss of process liquid because the surfaces of the particles of waste solids that are disposed of will typically be covered by or immersed in process liquid to at least some degree.
Heating Fluid Composition
[0101] The heating fluid is comprised of components that are less volatile than the process liquid, immiscible with the salt solvent, and selected from one or more of the following groups: unrefined hydrocarbon oils including undistilled crude oil, diesel, fuel oil, middle distillate, one or more other distilled crude oil fractions; refined hydrocarbon oils including base oil, hydrocracked base oil; synthetic oils and silicone oils; non-hydrocarbon oils including vegetable oils, seed oils, fish oils, bio-diesel, other animal oils; fatty acids including oleic acid, erucic acid, other fatty acids; heat transfer fluids including those used in solar energy facilities; hydraulic oils, lubricating oils and transmission fluids; liquid metals including gallium and gallium alloys, woods metal, lead tin bismuth alloys, fusible alloys; ionic liquids; deep eutectic solvents; other fluids whose volatility is negligible or at least low enough to avoid excessive vaporisation.
[0102] Some types of fluids have been recently discovered or invented, including many ionic liquids and deep eutectic solvents. These fluids may not yet be suitable for widespread deployment due to high cost, however they are the subject of extensive ongoing research. A non-limiting range of such fluids proposed for heat transfer applications, which might at some time in the future include potential use as components of the heating fluid in the present disclosure, is described in WO2017/085600.
Heating Fluid Treatment Means (HFTM)
[0103] The quality of the heating fluid can deteriorate over time due to its repeated mixing with contaminated process liquid. HFTM are included in this disclosure to maintain or enhance the quality of the heating fluid.
[0104] In the non-limiting example of MEG reclamation, as described above, most of the contaminants comprise water soluble salts that can be removed by including water as a component, possibly the only component, of the salt solvent. However, there can be numerous other types and sources of contamination of the heating fluid, as discussed below.
[0105] The heating fluid is continuously being mixed with more and more contaminants, day after day. These contaminants can accumulate and cause undesirable changes to the heating fluid properties such as its thermal stability, chemical stability, density, acidity, alkalinity, viscosity, boiling point, solubility, thermal conductivity, heat capacity, corrosivity, toxicity, flammability and/or surface tension. In the example of MEG reclamation, upstream systems that normally intercept or counteract contaminants (e.g. filters, chemical dosing treatments) may fail or be overwhelmed by unusual process conditions, thereby allowing slugs of contaminating substances to enter the reclamation facility and mix with the heating fluid.
[0106] The prior art does not include means to avoid or rectify contamination, deterioration and degradation of the heating fluid. Means to preserve or enhance the quality of the heating fluid are desirable so that it can be used repeatedly over and over again for months or years. If a user has to frequently discard heating fluid due to deterioration of its quality and replace it with new clean heating fluid, or alternatively has to send it elsewhere to be cleaned up, then that can be costly. The present disclosure reduces or avoids these costs by including a range of optional means to treat the heating fluid and extend its lifetime.
[0107] Some contaminants may form an unwanted sludge or rag layer. Asphaltenes, resins, waxes and/or other organic contaminants, including those that flow from the wells, may form sticky substances that adhere to equipment surfaces and foul heaters or form troublesome sludge and gum up instrumentation. Contaminants may flow out of the of the separation vessel with the vapour stream and then re-contaminate the condensed process liquid. Contaminants may be created by the oxidation or thermal degradation of the process liquid or the heating fluid itself. Contaminants may react with the process liquid or the heating fluid to form substances that are difficult to remove.
[0108] Mercury is a toxic substance that can contaminate the fluids entering a MEG reclamation facility.
[0109] Oxygen which can enter in dissolved form in rich MEG or dissolved in added liquids or enter due to air leaks, can accelerate corrosion and the degradation of some process liquids including MEG.
[0110] Ions of calcium, sodium, potassium, barium, iron, strontium, magnesium and the like can combine with carbonate, bicarbonate, hydroxide, sulfide, and/or sulfate ions to form precipitates that cause scaling and fouling. The accumulation of acids in the heating fluid may cause or accelerate corrosion. Fine particles of contaminants such as clays may become trapped in foams or emulsions in the heating fluid. The ingredients in chemical substances (e.g. corrosion inhibitor, dispersant, demulsifier, defoamer, pH control agent, scale inhibitor) that have been added to the process liquid before it enters the apparatus used to perform the present disclosure can be carried into the heating fluid and cause unwanted changes to its properties or otherwise impair its performance.
[0111] The HFTM include means to avoid or rectify these problems. The range, types and capacities of the HFTM are expected to vary to match the nature of and severity of contamination and degradation encountered in each particular application.
[0112] The present disclosure enables the inclusion of any one or more HFTM selected from the following list: [0113] Adding one or more substances and mixing the added substances with at least a portion of the heating fluid to achieve any one or more of the following effects: to cause a reaction with carbonate and/or bicarbonate contaminants thereby converting at least some of the contaminants into water and/or carbon dioxide; to reduce the oxygen content of the heating fluid; to remove and/or dissolve and/or destroy asphaltenes, resins, gums and/or sludges; to prevent or inhibit the formation of, or enable the removal of, scale or fouling deposits on metal surfaces; to break-down, suppress, or inhibit the formation of, emulsions or foam (e.g. by adding demulsifier or defoamer); to reduce the cloud point and/or freezing point of liquid contaminants; to neutralise acids and/or increase alkalinity and/or inhibit corrosion; to react with dissolved contaminants and cause precipitation of solid matter that can be removed by mechanical means of separation; and to modify one or more of the properties of the heating fluid including but not limited to density, vapour pressure, viscosity, thermal stability, pH, solubility, heat capacity, corrosivity, thermal conductivity, toxicity, and flammability. The added substances may be added to the heating fluid directly or be added to any of the streams that come into contact with the heating fluid. [0114] Removing at least a portion of the heating fluid and replacing said portion with heating fluid having enhanced properties. [0115] Removing mercury from the heating fluid. [0116] Removing liquid contaminants in liquid form from the flash separator. [0117] Heating at least a portion of the heating fluid to a temperature that causes liquid contaminants to vaporise and flow out of the flash separator. [0118] Operating the flash separator at a temperature and pressure that causes or promotes the break-down of emulsions and/or foams. [0119] Applying an electric charge or current to or across at least a portion of the heating fluid to cause ions of contaminating substances to migrate towards electrodes and thereby be removed. [0120] Removing contaminating particles of solid matter by mechanical means of separation including but not limited to any one or more of: centrifuging, settling, clarifying, filtering, and hydrocycloning, at least a portion of the heating fluid. If necessary, chemicals may be added that cause fine particles of contaminants to flocculate or agglomerate into larger masses that can be removed by mechanical means of separation. [0121] Removing acetate and possibly other organic salt contaminants by mixing acidic solutions, e.g. dilute hydrochloric acid, with at least a portion of the heating fluid to cause a reaction that converts at least a portion of the organic salts into volatile organic acids which can then be vaporised and removed.
Stage A plus Stage C Configuration
[0122]
[0123] Stream 20 comprises the concentrated process liquid that is produced in Stage A and flows into Stage C and is thereby a non-limiting example of what is herein termed the “Stage A output stream”. The Stage A output stream does not necessarily flow immediately from Stage A into Stage C. It can, for example, flow into an intermediate tank, and from there, or from any other suitable location, flow into Stage C. A person skilled in the art will recognise that the Stage A process, which comprises the steps leading up to the creation of the output stream 20 as shown in
[0124] Alternative means of separating water from aqueous process liquid solutions to produce a concentrated process liquid may also be feasible (e.g. molecular sieve, membranes).
[0125] Stage A Concentration comprises a process that precedes Stage B or Stage C and removes water from the feed stream by any feasible means to produce an output stream of concentrated process liquid.
[0126] In one or more embodiments Stage A operates at atmospheric pressure while in other embodiments Stage A operates under vacuum. Operation under vacuum reduces the boiling point of water and can enable Stage A to achieve higher process liquid concentrations at lower temperatures.
[0127] With reference to
[0128] Sufficient heat is added to the heating fluid in heater 24 and/or by heating the heating fluid within flash separator 21 to cause at least a portion of the process liquid in stream 20 to vaporise when stream 20 contacts heated heating fluid.
[0129] In embodiments at least all but a negligible remnant, of the process liquid in stream 20 is vaporised as a result of the contact between stream 20 and the heated heating fluid.
[0130] In an embodiment over 95%, or preferably over 98%, of the process liquid in stream 20 is vaporised as a result of the contact between stream 20 and the heated heating fluid.
[0131] Further descriptions of this configuration of the present disclosure are presented above under the headings Separation and Removal of Contaminants, Heating Fluid Composition, and Heating Fluid Treatment Means.
[0132] In the Stage A plus Stage C configuration of the present disclosure the flowrate of the stream entering the Flash on Heating Fluid process (i.e. stream 20) can be substantially less than the flowrate of the feed stream 10. This is possible because the feed stream 10 first enters Stage A which preferably removes most of the water thereby significantly reducing the quantity of liquid that enters the Flash on Heating Fluid process. This can substantially reduce the amount of heat needed to drive the Flash on Heating Fluid process when compared to the prior art (e.g. U.S. Pat. Nos. 8,652,304 and 10,328,360). The heat that is saved in Stage C is approximately equal to the heat that is applied in Stage A. However applying this heat in Stage A enables the use of simpler, lower cost equipment because in Stage A the water can be vaporised at a lower temperature than what is needed to vaporise the less volatile process liquid. Furthermore, the heat of vaporisation of water is substantially greater than that of many process liquids which is another reason to apply such heat using the lower cost Stage A method.
[0133] In the non-limiting example of MEG reclamation there are existing gas production sites where it is necessary to treat a salty dilute rich MEG solution (i.e. the feed stream) flowing at 10 m.sup.3/h or more. Consider a scenario in which the Stage A plus
[0134] Stage C configuration of the present disclosure is used to treat a feed stream 10 having a MEG concentration of 30% and flowing at 10 m.sup.3/h into Stage A. Stage A would reconcentrate the MEG solution to 90% concentration by vaporising (in reboiler 12) and removing (in stream 14) about 6.6 m.sup.3/h of water. This requires about 4.5 MW of heat to be provided via reboiler 12. This results in a flow of 90% concentrated MEG of about 3.4 m.sup.3/h (10 m.sup.3/h less 6.6 m.sup.3/h) entering Stage C via stream 20, which equates to a 66% smaller flow rate compared to feed stream 10. Stream 20 also comprises salts and other non-vaporised contaminants that had originally been in feed stream 10.
[0135] The Stage C Flash on Heating Fluid process in this configuration requires only approximately 1.2 MW of heat to vaporise MEG and water from stream 20, and thereby precipitate and remove monovalent salts (e.g. sodium chloride) and divalent ions (e.g. calcium, magnesium) that had originally been in stream 10. In embodiments Stage C vaporises at least all but a negligible remnant of the MEG in stream 20.
[0136] For the example described above the total heat required to fully vaporise the water and MEG in stream 10 would be about 5.7 MW but only 1.2 MW of this heat is needed for Stage C because 4.5 MW is provided in Stage A. By comparison the prior art versions of the Flash on Heating Fluid process (e.g. U.S. Pat. Nos. 8,652,304 or 10,328,360) would require 5.7 MW of heat to remove a similar amount of salt.
[0137] The significantly lower heat demand in the Stage C Flash on Heating Fluid process compared to the prior art yields a corresponding reduction in the quantity of heating fluid needed which reduces the cost to purchase and maintain or upgrade the pool of heating fluid and enables the use of smaller and less costly equipment (e.g. pumps, valves, pipes and heaters) to pump and heat the heating fluid.
[0138] There is also a reduction in electrical energy demand. The main consumer of electric power in the Stage A plus Stage C configuration illustrated in
Stage B plus Stage C Configuration
[0139]
[0140] Feed stream 10 comprises water, a water soluble process liquid that is less volatile than water, dissolved contaminants including monovalent salts (e.g. sodium chloride), divalent ions (e.g. calcium and magnesium), and organic salts (e.g. acetate), and liquid contaminants.
[0141] Stream 10 enters the Stage B separation vessel 51 through one or more entrance ports. The liquid pool in the lower part of Stage B separation vessel 51 contains a liquid which is comprised of concentrated process liquid. Stage B pump 53 draws concentrated process liquid out of the liquid pool in Stage B separation vessel 51 and pumps it through Stage B heater 54 to create a stream 55 of heated concentrated process liquid. Stream 55 and stream 10 directly contact each other in one or more places upstream of and/or within Stage B separation vessel 51. For example there may be one or more mixing zones or chambers upstream of Stage B separation vessel 51 into which both stream 10 and stream 55, or portions thereof, flow and mix with each other, and/or there may be multiple entrance ports into Stage B separation vessel 51 for both stream 10 and stream 55 thereby causing the two streams or portions thereof to mix with each other inside Stage B separation vessel 51 and/or stream 10 or a portion thereof, may enter the liquid pool in Stage B separation vessel 55 and therein contact heated concentrated process liquid.
[0142] Sufficient heat is added to the stream of concentrated process liquid in Stage B heater 54 to cause at least a portion of the water and process liquid in stream 10 to vaporise when stream 10 and stream 55 contact each other.
[0143] Vapour, which comprises vaporised process liquid and water and optionally liquid contaminants, exit the Stage B separation vessel 51 and flow via stream 56 into the Stage B distillation system 57. A person skilled in the art will recognise that separation and condensation of components of the vapour can be achieved using standard methods (e.g. vacuum distillation). The Stage B distillation system 57 includes equipment to enable operation of Stage B separation vessel 51 at sub-atmospheric pressure. Stream 58 comprises non-condensed gases and vapour that are subsequently removed. Stream 59 is an output product stream that may comprise process liquid that is depleted of salts and other contaminants. Stream 60 is optional and may comprise condensed liquid contaminants (if present) that are subsequently removed.
[0144] A second output stream 70 may convey contaminated process liquid into Stage C thereby moving salts and possibly other contaminants out of Stage B and into Stage C wherein they will be separated and removed. The term “Stage B to C stream” as used herein means the stream (for example stream 70) that conveys a mixture comprising at least a portion of the contaminants and at least a portion of the unvaporised process liquid from Stage B into Stage C.
[0145] Stage B differs markedly from the prior art versions of the Flash on Process Liquid process. In said prior art (U.S. Pat. Nos. 6,685,802 and 8,728,321) the process proceeds beyond the point that salts and other dissolved substances precipitate and begin to accumulate in the large pool of concentrated process liquid in the separation vessel. The rate of salt accumulation can be massive in MEG reclamation systems (e.g. over 5 tonnes per day). In the absence of further steps the accumulation of precipitated salts can rapidly become intolerable and cause a shutdown of the reclamation system. For this reason the prior art relies on mechanical means to separate the large quantities of precipitated solid matter from the concentrated process liquid (e.g. settling tank, clarifier, filter, centrifuge, salt downcomer).
[0146] In contrast, in this Stage B plus Stage C configuration of the present disclosure the precipitation of salts is controlled such that there is no excessive accumulation of precipitated solid matter in Stage B. Hence the present disclosure enables the deletion of the mechanical separation systems from the Flash on Process Liquid process, thereby significantly reducing complexity and cost. The avoided equipment which can include centrifuge, settling tanks, filters, salt tank, downcomer etc is typically large, complex, heavy, expensive to purchase, operate and maintain. The deletion of this equipment results in a simpler safer system that can be built and operated at lower cost. Salts must be removed but this is primarily done using simpler, lower cost, non-mechanical means in the Stage C Flash on Heating Fluid process that reduce the risk of loss of process liquid and harm to the environment.
[0147] In the non-limiting example of MEG reclamation sodium chloride, potassium chloride and optionally other monovalent salts precipitate and form a slurry with concentrated MEG in the liquid pool of the Stage B separation vessel 51. However divalent ions remain dissolved in the concentrated MEG thereby avoiding the risk of divalent ions combining with MEG to form unwanted complex compounds (e.g.
[0148] calcium-MEG-chloride, magnesium-MEG-chloride) which are known to person skilled in the art as particularly problematic in MEG reclamation systems. This divalent ion problem is discussed in Reference 1. The present disclosure avoids said divalent ion risks by ensuring that there is a sufficient flow of the mixture of salts and process liquid from Stage B via stream 70 into Stage C.
[0149] The present disclosure includes means to directly control the flow rate in stream 70 thereby preventing unwanted accumulation of divalent ions in Stage B. This feature adds considerable value to the present disclosure which can be illustrated by considering the non-limiting example of MEG reclamation. Consider the same scenario described earlier namely a 10 m.sup.3/h feed stream 10 comprising 30% MEG. This feed stream also contains 20 g/ltr of monovalent salts and 1 g/ltr of divalent ion salts. These salt concentrations are typical of many gas production sites worldwide where saline formation water is produced with the natural gas.
[0150] Steady flow at the above conditions results in a daily monovalent salt load of about 4,800 kg/d and a divalent ion salt load of about 250 kg/d. For these conditions the stream 70 flow can be regulated to maintain a flow rate of about 1 m.sup.3/h. This flow may appear small but it is high enough to ensure that the precipitated monovalent salt concentration in the Stage B separation vessel 51 remains below about 7 vol %. This is readily tolerable given that many existing MEG reclamation systems routinely work with MEG salt slurries having higher salt concentration. This flow is also sufficient to ensure that the divalent ions (especially calcium) remain dissolved at a concentration of less than about 4 g/ltr. This concentration of divalent ions in the pool of concentrated MEG in Stage B separation vessel 51 is readily tolerable and well below the suggested limit of 10 g/ltr proposed by experienced MEG reclamation system designers and operators (reference 1).
[0151] Stream 70 enters the flash separator 21 through one or more entrance ports. The liquid pool in the lower part of the flash separator 21 contains heating fluid, which is comprised of liquid components that are less volatile than the process liquid. Pump 23 draws heating fluid out of the flash separator 21 and pumps it through heater 24 to create a stream 25 of heated heating fluid. Stream 25 and stream 70 directly contact each other in one or more places upstream of and/or within flash separator 21. For example there may be one or more mixing zones or chambers upstream of flash separator 21 into which both stream 70 and stream 25, or portions thereof, flow and mix with each other, and/or there may be multiple entrance ports into flash separator 21 for both stream 70 and stream 25 thereby causing the two streams or portions thereof to mix with each other inside flash separator 21. Alternatively stream 70 or a portion of it may enter the liquid pool in flash separator 21 and therein contact heated heating fluid.
[0152] Sufficient heat is added to the heating fluid in heater 24 and/or by heating the heating fluid within flash separator 21 to cause at least a portion of the process liquid in stream 70 to vaporise when stream 70 contacts heated heating fluid.
[0153] In embodiments at least all but a negligible remnant, of the process liquid in stream 70 is vaporised as a result of the contact between stream 70 and the heated heating fluid.
[0154] In an embodiment over 95%, or preferably over 98%, of the process liquid in stream 70 is vaporised as a result of the contact between stream 70 and the heated heating fluid.
[0155] Further descriptions of this configuration of the present disclosure are presented above under the headings Separation and Removal of Contaminants, Heating Fluid Composition, and Heating Fluid Treatment Means.
[0156] When compared to the Stage C system in the Stage A plus Stage C configuration the Stage C system in the Stage B plus Stage C configuration is more compact and consumes even less energy. Consider the same MEG reclamation scenario as described previously i.e. the Stage B plus Stage C configuration is used to treat a 10 m.sup.3/h feed stream having a MEG concentration of 30%. Stage B comprises a Flash on Process Liquid process to produce an output product stream 59 comprising salt depleted (or salt free) concentrated MEG. This requires about 5.4 MW of heat that may be provided via the Stage B heater 54.
[0157] Stream 70 carries salts, possibly other contaminants and concentrated MEG from Stage B to Stage C at a flow rate of about 1.0 m.sup.3/h, which is 90% lower than the feed stream 10 flow rate of 10 m.sup.3/h. As a result of being able to operate Stage C at such a low flow rate, the amount of heat needed in Stage C is only about 0.3 MW. Stage C precipitates and removes monovalent salts (e.g. sodium chloride) and divalent ions (e.g. calcium and magnesium) that had originally been in stream 10. In embodiments Stage C vaporises at least all but a negligible remnant of the MEG in stream 70.
[0158] For the example described above the total heat required to fully vaporise the water and MEG in stream 10 is about 5.7 MW, which is approximately what would need to be provided when applying only the Flash on Heating Fluid process described in the prior art (e.g. U.S. Pat. Nos. 8,6752,304 or 10,328,360). By comparison the Flash on Heating Fluid process in this Stage B plus Stage C configuration only requires 0.3 MW of heat.
[0159] The significantly lower heat demand in the Stage C Flash on Heating Fluid process compared to the prior art yields a corresponding reduction in the quantity of heating fluid needed which reduces the cost to purchase and maintain or upgrade the pool of heating fluid.
[0160] It is possible to use the method of the present disclosure in a batch or continuous manner.
[0161] Persons of ordinary skill can utilise the disclosures and teachings herein to produce other embodiments and variations without undue experimentation. All such embodiments and variations are considered to be part of the present disclosure. Accordingly, one of ordinary skill in the art will readily appreciate from the disclosure that later modifications, substitutions, and/or variations performing substantially the same function or achieving substantially the same result as embodiments described herein may be utilised according to such related embodiments of the present disclosure. Thus, the disclosure is intended to encompass, within its scope, the modifications, substitutions, and variations to processes, manufactures, compositions of matter, compounds, means, methods, and/or steps disclosed herein. The description herein may contain subject matter that falls outside of the scope of the claimed disclosure. This subject matter is included to aid understanding of the disclosure.
[0162] In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present disclosure. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.
Reference
[0163] 1. “Removal of Divalent Salts from Aqueous MEG Solutions in a MEG Reclamation System”, GPA Europe Annual Conference, September 2011, Simon Crawley-Boevey